Conventionally, as a typical inverter main circuit construction, a construction for once converting a commercial alternating current into a DC voltage via a rectifying circuit and a smoothing circuit and obtaining an AC voltage by a voltage-fed inverter section is generally employed. In this case, the smoothing circuit needs large-scale capacitor and reactor for smoothing voltage pulsations at the commercial frequency, and this therefore causes an increase in volume and a cost increase of the inverter section. Therefore, a main circuit construction for compacting the LC filter and suppressing only the carrier current component of the inverter is proposed. (Refer to, for example, “3. Direct AC power converter circuit (present condition and problems of a direct AC power converter circuit technology and related technologies)” of the 998th technical report of The Institute of Electrical Engineers of Japan (Reference Document 1)).
On the other hand, it is known that the DC voltage sometimes pulsates at the resonance frequency of the LC filter due to load fluctuations and output frequency fluctuations in the inverter that has the LC filter in the DC link part, and an inverter that detects the vibration components of a DC voltage by an HPF (high-pass filter) and suppresses the vibrations in a current control system on the inverter side is proposed. (Refer to, for example, JP H09-172783 A (Reference Document 2)).
The inverter that has the compacted LC filter in the DC link part is preconditioned so that the DC voltage is made to pulsate at a sixfold frequency of the power frequency, and the higher harmonic frequency of the power pulsation component and the resonance frequency of the filter become close to each other by the vibration suppression method described above. Accordingly, it is difficult to separate both of them from each other, and there is a problem that low-order distortions occur in the input current as a consequence of the smoothing of the DC voltage.